Since the deadly Marburg virus was first identified in 1967, there have been only six known outbreaks, mostly in Africa. Yet for victims and public health workers, that's plenty. Now a research team reports that a candidate Marburg vaccine given to monkeys shortly after infection fully protected them from the virus. The findings offer hope that public health workers and others in contact with Marburg victims could be similarly protected.
Like its cousin the Ebola virus, the Marburg virus causes symptoms that start off with fever and chills and often end with severe weight loss, massive internal bleeding, shock, multiorgan failure, and death. There is no treatment or cure: During the last outbreak, in Angola during 2004-2005, 89% of the more than 300 victims died (ScienceNOW, 29 March, 2005).
Last year, a team led by virologist Thomas Geisbert of the U.S. Army Medical Research Institute of Infectious Diseases (AMRIID) in Fort Detrick, Maryland, reported that it had created vaccines that protected rhesus monkeys against both Marburg and Ebola viruses when given before exposure. The vaccines were concocted by attaching proteins from the outer coat of the viruses to another microbe, called vesicular stomatitis virus (VSV), which had been weakened so that it would not cause disease.
A pre-exposure vaccine is of limited use in Africa however, because vaccinating entire populations against a rare virus is impractical. So Geisbert's team decided to see whether the vaccine would still work if given after exposure to Marburg. The researchers infected eight rhesus monkeys with a high dose of Marburg virus. About 20 to 30 minutes later, they injected five of the monkeys with the Marburg vaccine. The remaining monkeys were injected with the Ebola vaccine, to act as a control. Within 6 to 10 days, the control monkeys had developed fevers, and by 12 days, all three were dead from the infection. The Marburg-vaccinated monkeys, on the other hand, showed only minimal symptoms, and all survived.
Combined with the previous work, the study shows that the Marburg vaccine has potential "dual efficacy," both as a preventive and a postexposure treatment, the team reports online today in The Lancet. Although there are no immediate plans to test the vaccine in humans, the authors plan to study how long postinfection such a vaccine could protect against illness.
Simon Wain-Hobson, a virologist at the Pasteur Institute in Paris, says that the study is "good news." But he adds that the vaccine needs to be effective for much longer than 20 to 30 minutes after infection if it is to be useful. "You would have to be next door to the doctor with the vaccine loaded up and ready to go."